Surfacing MDF Spoil board issue

[bluehammer]

Hello All, I went to surface a new 4'x8' sheet of 1/2" MDF that is being used as my spoil board. Everything was going great until it got about 10" from the outer edge and the corners started to lift a good 1/4"-3/8". We started the surfacing in the center and cut outward. My assumption is it had a surface tension issue that caused the whole board to buckle and it lost its suction from the vacuum table. Needless to say it ruined the sheet of MDF. Any one have thoughts on how to avoid this? I was going to try again with a new sheet and start from the outer edge and work my way to the center, but figure I'd ask here to see if anyone had any thoughts. This is our first CNC so we are just learning.

 

[ikarasu]

MDF warps a lot in heat. Ours will look like a banana overnight if someone leaves the heat on. You can most the board and throw something heavy on it and leave it overnight and it'll re-form itself back into being flat. Our vacuum is strong enough to hold it down even when it's warped by a few inches though.

We surface from one edge to the other - only because that's the way our multicam machine was programmed to do it. Not sure if it'd help your particular problem ... But you can always try.

 

[Z SIGNS]

You don't usually machine a spoil board. It's usually a piece of coro or cardboard.
You surface your machine bed.
If it's MDF if it wants to be thicker so you resurface many times.
On the bright side now you know how to make a potato chip.

 

[MIKE MCNAMARA]

We use .125" MDF when we can get it and .25" typically. No resurfacing, toss it when both sides are carved up. If anything we might sand some slightly to knock off any crud, but the time it takes to resurface a 4x8 does not make sense to us. Also, I would think you get better suction hold down using a thinner mdf.

 

[GC Decor]

Use 3/4” - once you surface 1/2” you’ll see buckling because it’s thin. Try to find LDF as well, MDF has more glue and Moisture. Vacuum pumps we’ll have a harder time pull through it. Most cabinet materials suppliers will have it. LDF also tends to warp less, we tried several products over the year but that was the winner by far. It’s also 1/2 the weight so much easier to move around.

 

[GC Decor]

We use .125" MDF when we can get it and .25" typically. No resurfacing, toss it when both sides are carved up. If anything we might sand some slightly to knock off any crud, but the time it takes to resurface a 4x8 does not make sense to us. Also, I would think you get better suction hold down using a thinner mdf.

With vacuum hold down you would never use .125 or 1/4” - you have to surface Mdf for a vacuum table, they have a coating on each side that will eliminate the ability for air to pass through. You have to prevent dust from getting into your vacuum system, this can easily kill an expensive vacuum system.

 

[ikarasu]

Those of you who dont surface MDF....

Do you use a vacuum pump? MDF has a skin on it, and surfacing it breaks the skin and allows it to be more porous. You're "Supposed" to surface both sides and seal the edges for optimal suction...


I wish we could get LDF, I've heard great things about it but cant get it locally without paying a huge price

 

[bluehammer]

Thanks Everyone. I'm going to try 3/4" MDF and start from the outside. I'll keep you posted.

 

[MikePro]

whenever I replace my MDF spoilboard, i surface one side of the panels to be replaced and tack that side-down in place of the old spoilboard onto my bed with carpet tape (keeps from sliding around when vacuum is off). I then machine the opposite side after securing it to my table.

Huuuuuge difference in vacuum draw once you break that factory finish-"skin".
My table surface would always potatochip like craaaaazy once it got thinner than ~.25" but ever since I started doing the double-surfacing about 15yrs ago, i can run my spoilboard til it is less than 1/8" thick until I replace my MDF about every 6-10months with .5"/.75" depending what's avail.

 

[packratsigns]

We use Ultralight MDF Board 3/4" - 4' x 8' (actually larger in some cases). Nylon screws to hold it down. 1/4"-20 tapped into the phenolic. We use a large 2.5" Amana spoilboard tool to surface. Lasts for months.

​

 

[bluehammer]

whenever I replace my MDF spoilboard, i surface one side of the panels to be replaced and tack that side-down in place of the old spoilboard onto my bed with carpet tape (keeps from sliding around when vacuum is off). I then machine the opposite side after securing it to my table.

Huuuuuge difference in vacuum draw once you break that factory finish-"skin".
My table surface would always potatochip like craaaaazy once it got thinner than ~.25" but ever since I started doing the double-surfacing about 15yrs ago, i can run my spoilboard til it is less than 1/8" thick until I replace my MDF about every 6-10months with .5"/.75" depending what's avail.

So do you tape it down BEFORE surfacing the first side? Do you also tape it down when surfacing the second side?

 

[fixtureman]

I use Trupan Mdf from Arauco for my spoil board haven't had a problem with it

 

[MikePro]

So do you tape it down BEFORE surfacing the first side? Do you also tape it down when surfacing the second side?

nah, i don't tape for the sake of surfacing. i surface one side of my new boards before removing the old ones, and then carpet tape that side-down before finishing with a surfacing of the 2nd side that will be my table top.

I've heard people use nylon screws, but i've always just used tape and it only gets messy after a few replacements when I take the extra time to finally scrape-up the multiple layers of carpet tape that has accumulated.

 

[GaSouthpaw]

I would definitely start with a 3/4" thick spoil board. Once ours gets to 1/2", it's time to order a new one (in Georgia, where heat and humidity wreak havoc on them). When it's new, we remove about .005" from the first side (with the old board still on the table), then remove the old board, flip the new one, and remove the same .005" or so.
Many of the table manufacturers also suggest "sealing" the edges with paint or stain. I find we don't lose that much vacuum this way, so it's not worth the time (for us, not saying it's never worth it). We also make sure to use the correct gasketing in the channels of the table's phenolic base.

 

[bluehammer]

nah, i don't tape for the sake of surfacing. i surface one side of my new boards before removing the old ones, and then carpet tape that side-down before finishing with a surfacing of the 2nd side that will be my table top.

I've heard people use nylon screws, but i've always just used tape and it only gets messy after a few replacements when I take the extra time to finally scrape-up the multiple layers of carpet tape that has accumulated.

I used your method and it worked great. Thanks!